Signals are communicated via communication channels, such as signal lines. Data bits may be transmitted via a communication channel by a driver using pulse amplitude modulation (PAM). A receiver typically recovers the transmitted data appropriately sampling and quantizing the received signals.
Transmission impairments, such as dispersion and attenuation in communication channels, often limit the edge rates of a received signal relative to the bit-time. In these band-limited systems, inter-symbol-interference (ISI) occurs when the residue power from previous bits interferes with the current bit being received. Interference can also arise from inductive or capacitive crosstalk caused by other signal lines. Such signal impairment reduces the voltage margin at the receiver and consequently increases the bit-error rate, as evidenced by a reduction of an opening in a so-called eye pattern, which is generated by synchronously overlapping edges in the received signals and which indicates the signal health. Such interference can worsen as the data-rate increases, especially in systems that use PAM with more than two levels (so-called multi-level PAM or multi-PAM).